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Sequence of tenses

My problem today is that I don't seem to fully understand when I am supposed to "backshift" the tense.

I understand this:
He said he was in a bad mood at the party. (The party is over, it refers to the past, that's why I use '... was in a bad mood.'

Or this:

He thought I would phone him, but I didn't. (It refers to the past that's why I used future in the past.)

But what happens if the thing I'm referring to is still future at the time of speaking.

Eg: He said his Mum will be 50 on 15 December. (Today is 3 Dec)
Am I supposed to say?:

'He said his Mum would be 50 on 15 December.' or it is okay-ish the way I expressed???

Or: Tomorrow is Tuesday. He said tomorrow is / was / would be Tuesday???
Or: My colleague tells me that there will be no one waiting for me at the airport when I arrive tomorrow. I react immediately.
What do I say?

I thought someone will / would be waiting for me when I arrive tomorrow.

Or: On Wednesday, there will be a match. Someone tells me it starts at 8:00pm. I'm all: 'I thought it starts / started / would start at 9:00'???

So, the question is: Do I ALWAYS have to backshift the tense?
Or it is only important when I talk about something that happened in the past? Oh, I'm confused. Please help.